The present invention relates to a method and apparatus capable of non-invasively determining the highest and lowest values for systolic and diastolic blood pressures, as well as a typical blood pressure value. While not so limited, the method and apparatus of the present invention is particularly useful for obtaining the foregoing blood pressure measurements from patients in which blood pressures vary significantly from heartbeat to heartbeat, such as patients in atrial fibrillation. The determination may be carried out in a single non-invasive blood pressure measurement procedure.
The determination of blood pressure is a basic physiological measurement. It indicates the forces exerted on the blood vessels of the circulatory system by the pumping, or beating, action of the heart. The repeated pumping action of the heart causes the pressure within the blood vessels to cyclically increase and decrease. Blood pressure is typically expressed in terms of the highest pressure observed during a cycle and the lowest level of pressure observed during a cycle. The former is termed “systolic” pressure, the latter is termed the “diastolic” pressure, and the indication of blood pressure at the end of a measurement procedure is commonly expressed as a combination of the two pressures, i.e. “110/70” or “110 over 70”, it being understood that the units of pressure are millimeters of mercury (mm Hg).
Blood pressure may be determined by means of auscultation, in which a blood vessel, typically the brachial artery in the upper arm, is occluded by a pressurized cuff, and the sounds of the blood moving through the blood vessel are detected with a stethoscope as the pressure in the cuff is reduced. The cuff pressures at appearance and disappearance of these sounds as the cuff is deflated from the occluding state are indications of the systolic and diastolic pressures. Or, blood pressure can be measured by an oscillometric technique in which a blood vessel is occluded and the magnitude of the pulsations of the blood in the blood vessel is measured as the pressure in the cuff is lessened. The pattern of increase and decrease in oscillation size as the cuff pressure changes can be used to estimate systolic, mean arterial, and diastolic blood pressures. Oscillometry is often used in blood pressure monitors because it lends itself to being carried out by automated instrumentation.
For auscultation, the values that are presented for the systolic and diastolic blood pressures depend, to a considerable extent on the skill and predilection of the clinician, whereas for oscillometry, the reported values are based on the assumptions and structure built into the instrumentation algorithm. In both cases, the expressed systolic and diastolic pressures values are commonly thought of as being found in each of a succession of heartbeats occurring over an extended period of time. This permits such blood pressure values to serve as a basis for screening and treatment. But as a result, extreme values may not be fully reflected in the blood pressure determination because of an effort to provide what is seen as the most representative, and generally more useful, blood pressure values.
However, as noted above, there are medical conditions in which a patient's blood pressure is changing by large amounts on almost every beat of the heart. One such condition is irregularity in the rhythms of the heartbeat, such as is found in patients with atrial fibrillation. In these patients, it is clinically significant not only to know typical blood pressure values, but also to know the extremes, i.e. highest and lowest systolic and diastolic blood pressure values seen in the patient.